1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine, and particularly, to control of fuel injection in starting an internal combustion engine having a first fuel injection mechanism (an in-cylinder injector) for injecting fuel into a cylinder and a second fuel injection mechanism (an intake manifold injector) for injecting the fuel into an intake manifold and/or an intake port.
2. Description of the Background Art
With an internal combustion engine having an in-cylinder injector for injecting fuel directly into a combustion chamber and an intake port injector for injecting fuel into an intake port of each cylinder, when combustion is carried out by injecting fuel solely from the intake port injector, the in-cylinder injector is always exposed to combustion gas of high temperature without being cooled by means of vaporization of the injected fuel. Thus, the temperature of the tip thereof is constantly high, and deposits are likely to accumulate in the injection hole.
Accordingly, a control apparatus has been proposed that opens an intake port injector to inject fuel into an intake port and that concurrently opens an in-cylinder injector to inject fuel into a combustion chamber in a homogeneous combustion drive mode, in order to prevent the tip of the in-cylinder injector from being constantly at high temperatures (for example, Japanese Patent Laying-Open No. 2002-364409). That is, it is preferable to secure fuel injection from the in-cylinder injector in the homogeneous combustion drive mode where the engine is in a warm state.
On the other hand, vaporization of fuel inside the cylinder is hardly facilitated at low temperatures. Therefore, if fuel is injected from the in-cylinder injector at low temperatures, the injected fuel is likely to adhere to a top of an engine piston (a piston top) or to an internal peripheral surface inside cylinder (a cylinder internal peripheral surface (bore)) in a large amount. The fuel adhered to the piston top gradually vaporizes in the following combustion in the engine resulting in incomplete combustion, whereby deterioration of exhaust gas emission, such as generation of black smoke and an increase in uncombusted components, is invited. The fuel adhered to the cylinder internal peripheral surface mixes with and dilutes lubricant oil applied to the surface for lubricating the piston, and thus may impair the lubrication performance. Accordingly, it is preferable to minimize the fuel injection from the in-cylinder injector in the homogeneous combustion drive mode where the engine is in a cold state.
In an internal combustion engine where the in-cylinder injector and the intake manifold injector are both employed, it is necessary to set a fuel injection ratio between the injectors in accordance with a condition of the engine (such as temperature, engine speed and load). In particular, as the engine output condition is uniform in starting the engine, it is necessary to appropriately set the fuel injection ratio in accordance with the engine temperature.
The setting of the fuel injection ratio in starting the engine, i.e., a fuel injection ratio initial setting is generally executed as part of a starting sequence on power-up of a control apparatus (ECU: Electronic Control Unit). However, such a setting scheme does not ensure preferable initial setting if there is a delay between the power-up of the ECU and actual start of the engine. Thus, there still remains a possibility that the combustion state of the engine is deteriorated and the engine cannot be started smoothly.